Golf ball

ABSTRACT

A golf ball has arranged thereon one or more dimples having a cross-sectional shape specified by a particular sequence of steps, and the total number of dimples on the ball surface is from 250 to 380. This ball has a reduced air resistance during flight, enhancing the aerodynamic performance and enabling an increased distance to be achieved.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2016-250588 filed in Japan on Dec. 26,2016, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a golf ball having numerous dimples formed onthe surface thereof. More particularly, the invention relates to a golfball whose aerodynamic performance has been enhanced by optimizing thecross-sectional shape of the dimples formed on the ball surface.

BACKGROUND ART

To increase the distance traveled by a golf ball, it is important bothto increase the rebound of the ball and also to reduce the airresistance during flight by means of dimples formed on the ball surfaceand thus improve the aerodynamic performance. This fact is generallywell known, which is why, for example, many golfers use golf balls onwhich have been formed numerous dimples that are circularly arcuate incross-section as shown in FIG. 5. In order to further enhance theaerodynamic performance of the ball, various disclosures concerning thedimple shape and the method of configuring the dimples have hithertobeen made in, for example, JP-A H11-57065, JP-A 2005-342407, JP-A2006-149929, JP-A 2006-158778, JP-A 2006-187476, JP-A 2006-187485 andJP-A 2008-93481.

U.S. Pat. Nos. 8,888,613 and 8,974,320 describe golf balls in which,when deciding on the cross-sectional shape of a dimple, a distinctivecross-sectional curve shape is obtained by dividing the interior of thedimple into a plurality of specific regions and quantifying the dimpleinterior in such a way that the average depth in each region satisfies aspecific relationship. However, even such art does not sufficientlyimprove the distance of the golf ball, and so there remains room forimprovement in the aerodynamic performance and flight performance of theball. Nor have there existed many golf balls with numerous dimplesthereon of the above distinctive cross-sectional shapes.

Developing golf balls which enable more golfers to obtain a satisfactoryflight performance is important for expanding the golfer base, andfurther improvement in the aerodynamic performance of the ball isessential for achieving a better flight performance.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golfball which is able to further increase the aerodynamic performance ofthe ball and enhance the flight performance.

As a result of extensive investigations, the inventors have discoveredthat, when deciding on the cross-sectional shape of a dimple, by lettinga straight line that passes through any one point on the edge of thedimple and the foot of a perpendicular drawn from a deepest point of thedimple to an imaginary plane defined by the peripheral edge of thedimple serve as a reference line, dividing the reference line from thedimple edge at 0% (origin) to the foot at 100% into 20% segments, andsetting within a fixed range the change in dimple depth ΔH in dimpleregions that are divided into 20% each, the dimple cross-sectional shapestabilizes the dimple effect during flight of the ball, which iseffective for enhancing the aerodynamic performance.

That is, improving the aerodynamic performance of the ball is essentialfor achieving a. better flight performance. In this invention, thecross-sectional shape of the dimples is optimized even further than inthe prior art, thereby reducing the variability in flight and improvingthe aerodynamic performance. Moreover, the percentage change in depth atgiven positions in the dimple is held within a fixed range, whichstabilizes the dimple effect and enables the aerodynamic performance tobe improved.

Accordingly, the invention provides a golf ball having numerous dimplesformed on a surface thereof, wherein the ball has arranged thereon atleast one dimple with a cross-sectional shape that is described by acurved line or by a combination of a straight line and a curved line andis specified by steps (i) to (iv) below:

(i) letting the foot of a perpendicular drawn from a deepest point ofthe dimple to an imaginary plane defined by a peripheral edge of thedimple be the dimple center and a straight line that passes through thedimple center and any one point on the edge of the dimple be thereference line;

(ii) dividing a segment of the reference line from the dimple edge tothe dimple center into at least 100 points and computing the distanceratio for each point when the distance from the dimple edge to thedimple center is set to 100%;

(iii) computing the dimple depth ratio at every 20% from 0 to 100% ofthe distance from the dimple edge to the dimple center; and

(iv) at the depth ratios in dimple regions 20 to 100% of the distancefrom the dimple edge to the dimple center, determining the change indepth ΔH every 20% of this distance and designing a dimplecross-sectional shape such that the change ΔH is at least 6% and notmore than 24% in all regions corresponding to from 20 to 100% of thisdistance.

The total number of dimples on the surface of the ball is from 250 to380.

In a preferred embodiment of the golf ball of the invention, in dimpleshaving the specified cross-sectional shape, the change ΔH in dimpledepth reaches a maximum at 20% of the distance from the dimple edge tothe dimple center.

In another preferred embodiment of the invention, dimples having thespecified cross-sectional shape account for at least 60% of the totalnumber of dimples.

In yet another preferred embodiment, the dimples formed on the ballsurface are of at least two types of differing diameter and/or depth.

In a further preferred embodiment, the curved line describing thecross-sectional shape of the dimple includes two or more points ofinflection.

ADVANTAGEOUS EFFECTS OF THE INVENTION

The golf ball of the invention has at least one dimple of a distinctivecross-sectional shape which stabilizes the dimple effect during flightof the ball, enabling the aerodynamic performance to be furtherenhanced.

BRIEF DESCRIPTION OF THE DIAGRAMS

FIG. 1A is a plan view showing the outward appearance of a golf ballaccording to one embodiment of the invention, and FIG. 1B is an enlargedcross-sectional view of one of the dimples formed on the surface of thegolf ball shown in FIG. 1A.

FIG. 2 is a graph showing the relationship between the dimplecross-section and regions established at the interior of the dimple.

FIG. 3A is a plan view showing the outward appearance of a golf ballaccording to another embodiment of the invention, and FIG. 3B is anenlarged cross-sectional view of one of the dimples formed on thesurface of the golf ball shown in FIG. 3A.

FIG. 4A is a plan view showing the outward appearance of a golf ball onwhich conventional double dimples have been formed, and FIG. 4B is anenlarged cross-sectional view of one of the dimples formed on thesurface of the golf ball shown in FIG. 4A.

FIG. 5A is a plan view showing the outward appearance of a golf ball onwhich conventional dimples that are circularly arcuate in cross-sectionhave been formed, and FIG. 5B is an enlarged cross-sectional view of oneof the dimples formed on the surface of the golf ball shown in FIG. 5A.

FIG. 6 is a schematic cross-sectional view showing an example of thestructure of the inventive golf ball.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become moreapparent from the following detailed description, taken in conjunctionwith the foregoing diagrams.

FIG. 1A is a plan view showing the outward appearance of a golf ballaccording to one embodiment of the invention, and FIG. 1B is an enlargedcross-sectional view of one of the dimples formed on the surface of thegolf ball shown in FIG. 1A. In these diagrams, the symbol D represents adimple, E represents an edge of the dimple, P represents a deepest pointof the dimple, the straight line L is a reference line which passesthrough the dimple edge E and a center O of the dimple, and the dashedline represents an imaginary spherical surface. The foot of aperpendicular drawn from the deepest point P of the dimple to animaginary plane defined by a peripheral edge of the dimple D coincideswith the dimple center O. The dimple edge E is the boundary between thedimple D and regions (lands) on the ball surface where dimples D are notformed, and corresponds to points where the imaginary spherical surfaceis tangent to the ball surface (the same applies below). The dimple Dshown in FIG. 1 is a circular dimple as seen in a plan view; the centerO of the dimple in a plan view coincides with the deepest point P.

The cross-sectional shape of the dimple shown in FIG. 1B, which is notdrawn to scale, relies on a proper understanding of the invention. Thesame applies also to the cross-sectional shapes of the dimples shownsubsequently in FIGS. 2, 3B, 4B and 5B.

In the invention, it is critical for the cross-sectional shape of thedimple I to satisfy the following conditions.

First, as condition (i), let the foot of a perpendicular drawn from adeepest point P of the dimple to an imaginary plane defined by aperipheral edge of the dimple be the dimple center O, and let a straightline that passes through the dimple center O and any one point on theedge E of the dimple be the reference line L.

Next, as condition (ii), divide a segment of the reference line L fromthe dimple edge E to the dimple center O into at least 100 points. Thencompute the distance ratio for each point when the distance from thedimple edge to the dimple center is set to 100%. That is, referring toFIG. 2, the dashed lines in the chart are dividing lines representedalong the dimple depth. The dimple edge E is the origin, which is the 0%position on the reference line, and the dimple center O is the 100%position with respect to segment EO on the reference line.

Next, as condition (iii), compute the dimple depth ratio at every 20%from 0 to 100% of the distance from the dimple edge E to the dimplecenter O. In this case, the dimple center O is at the deepest part P ofthe dimple and has a depth H (mm). Letting this be 100% of the depth,the dimple depth ratio at each distance is determined. Also, the dimpledepth ratio at the dimple edge E becomes 0%.

Next, as condition (iv), at the depth ratios in dimple regions 20 to100% of the distance from the dimple edge E to the dimple center O,determine the change in depth ΔH every 20% of the distance and design adimple cross-sectional shape such that the change ΔH is at least 6% andnot more than 24% in all regions corresponding to from 20 to 100% of thedistance.

In this invention, by quantifying the cross-sectional shape of thedimple in this way, that is, by setting the change in dimple depth ΔH toat least 6% and not more than 24%. and thereby optimizing the dimplecross-sectional shape, the flight variability decreases, enhancing theaerodynamic performance of the ball. This change ΔH is preferably from 8to 22%, and more preferably from 10 to 20%.

Also, to further increase the advantageous effects of the invention, indimples having the specified cross-sectional shape, it is preferable forthe change in dimple depth ΔH to reach a maximum at 20% of the distancefrom the dimple edge to the dimple center. Also, the inclusion of two ormore points of inflection on the curved line describing the specifiedcross-sectional shape of the dimple is preferable in terms of increasingthe advantageous effects of the invention.

Dimples that are circular as seen in the plan view are depicted in FIG.1 by way of illustration, although the dimple shape (plan-view shape) isnot limited to a circular shape. Dimples of other shapes, such aspolygonal, teardrop or elliptical dimples, may be suitably selected.Even with dimples of non-circular shape, it is possible to set thecross-sectional shape by a method similar to that indicated above. Inthe example shown in FIG. 1, the center O and the deepest point P of thedimple coincide. However, the deepest point P does not necessarily haveto coincide with the center O of the dimple. Even when the center O andthe deepest point P of the dimple D do not coincide, this does not poseany particular problem; the change in dimple depth ΔH within dimpleregions that are divided into 20% each can be determined in the same wayas described above.

The cross-sectional shape of the dimple D is illustrated in FIG. 1 by ashape composed primarily of a gently curved line and including straightlines in portions thereof, but is not limited thereto so long as it is acurve within the scope of the invention that is described by a curvedline or by a combination of a straight line and a curved line.

The diameter of the dimple D (in polygonal dimples, the diagonallength), although not particularly limited, may be set to preferably atleast 1.5 mm, and more preferably at least 2.0 mm. There is noparticular upper limit, although the dimple diameter is preferably setto not more than 7.0 mm, and more preferably not more than 6.0 mm.

The dimple D has a depth H at the deepest point P thereof which,although not particularly limited, may be set to preferably from 0.05 to0.5 mm, and more preferably from 0.1 to 0.4 mm.

The method of configuring the dimples is not particularly limited,although preferred use may be made of a method which uses ageometrically configured pattern in the form of a regular polyhedronsuch as a regular octahedron, a regular dodecahedron or a regularicosahedron, or a method that involves configuring the dimples withrotational symmetry about the poles of the ball, such as three-foldsymmetry, four-fold symmetry, five-fold symmetry or six-fold symmetry.

The total number of dimples formed on the ball surface is set to atleast 250, preferably at least 275, and more preferably at least 300.The upper limit in the number of dimples is set to not more than 380,preferably not more than 370, and more preferably not more than 360.

In this invention, the dimples formed on the surface of the ball includeat least one dimple having the above-described cross-sectional shape,such dimples accounting for a portion of all the dimples. Accordingly,in this invention, it is not necessary for all the dimples formed on theball surface to be dimples having the above-described cross-sectionalshape, it being possible to intersperse conventional dimples. In such acase, the dimples having the above-described cross-sectional shapeaccount for a proportion of the total number of dimples formed on theball surface which, although not particularly limited, may be set to 20%or more, preferably 50% or more, more preferably 60% or more, even morepreferably 80% or more, and most preferably 100%.

In the invention, although not particularly limited, it is recommendedthat preferably at least two types, and more preferably at least threetypes, of dimples of mutually differing diameter and/or depth be formed.When conventional dimples which do not satisfy the above-describedconditions are included, if such dimples include ones of mutuallydiffering diameter and/or depth, they shall be regarded here asdiffering types of dimples.

The proportion SR (%) of the total surface area of the imaginaryspherical surface of the ball that is circumscribed by the edges of theabove dimples, sometimes referred to as the “dimple coverage ratio,” isgenerally at least 70%, and preferably at least 80%. At an SR valueoutside of this range, a suitable trajectory may not be obtained, whichmay result in a decreased distance.

The sum of the volumes of the individual dimple spaces formed below aflat plane circumscribed by the edge of each dimple, expressed as aratio VR (dimple spatial occupancy) with respect to the volume of animaginary sphere were the ball surface assumed to have no dimplesthereon, although not particularly limited, may be set to generally atleast 0.7%, preferably at least 0.75%, and more preferably at least0.8%, with the upper limit being preferably not more than 1.5%, morepreferably not more than 1.45%, and even more preferably not more than1.4%. By setting the dimple spatial occupancy VR in the above range,when the ball is struck with a distance club such as a driver, the shotcan be prevented from rising too steeply or from dropping withoutgaining enough height.

To fabricate a mold for molding the above golf ball, a technique may beemployed in which 3D CAD/CAM is used to directly cut the entire surfaceshape three-dimensionally into a master mold from which the golf ballmold is subsequently made by pattern reversal, or to directly cutthree-dimensionally the cavity (inside walls) of the golf ball mold.

As with conventional golf balls, various types of coatings, such aswhite enamel coatings, epoxy coatings and clear coatings, may be appliedto the ball surface. In such cases, to avoid marring the cross-sectionalshape of the dimples, it is desirable to evenly and uniformly coat thesurface.

The golf ball of the invention is not particularly limited with regardto the internal construction. That is, the present art may be applied toany type of golf ball, including solid golf balls such as one-piece golfballs, two-piece golf balls, and multi-piece golf balls having aconstruction of three or more layers, and also wound golf balls.Referring to FIG. 6, the use of a multi-piece solid golf ball Gin whichan intermediate layer 2 composed of one or more layers is formed betweena solid core 1 and a cover 3 is especially preferred. In FIG. 6, thesymbol D represents a dimple.

In the golf ball G shown in FIG. 6, the solid core 1 is preferablyformed primarily of polybutadiene. Also, the solid core 1 has adeflection when compressed under a final load of 1,275 N (130 kgf) froman initial load of 98 N (10 kgf) which, although not particularlylimited, may be set to preferably at least 2.0 mm and preferably notmore than 6.0 mm.

The materials used in the intermediate layer 2 and the cover 3 are notparticularly limited. Preferred use may be made of, for example, knownionomer resins, thermoplastic elastomers and thermoset elastomers.Exemplary thermoplastic elastomers include polyester, polyamide,polyurethane, olefin and styrene-type thermoplastic elastomers.

The material hardness of the intermediate layer, although notparticularly limited, may be set to a Shore D hardness of generally atleast 30 and generally not more than 75.

The material hardness of the cover, although not particularly limited,may be set to a Shore D hardness of generally at least 30 and generallynot more than 75.

The above material hardnesses are values obtained by using a moldingpress to mold the material into sheets having a thickness of 2 mm,stacking the molded sheets to a thickness of at least 6 mm, andmeasuring the hardness in accordance with ASTM D2240 with a type Ddurometer.

The thickness of the intermediate layer and the thickness of the cover,although not particularly limited, are each preferably set in the rangeof 0.3 to 3.0 mm. Ball parameters such as the weight and diameter may besuitably set in accordance with the Rules of Golf

As described above, the golf ball of the invention, by having dimples ofa characteristic cross-sectional shape formed on the surface thereof,has a reduced air resistance during flight. This improves theaerodynamic performance of the ball, enabling a higher trajectory to beachieved. As a result, the distance traveled by the ball can be furtherincreased.

EXAMPLES

Working Examples and Comparative Examples are given below by way ofillustration, although the invention is not limited by the followingExamples.

Working Examples 1 and 2, and Comparative Examples 1 and 2

Golf balls having the dimples shown in Working Example 1 (FIG. 1),Working Example 2 (FIG. 3), Comparative Example 1 (FIG. 4, conventionaldouble dimples) and Comparative Example 2 (FIG. 5, dimples that arecircularly arcuate in cross-section) formed on the hall surface weremanufactured, and the flight properties were compared. Four types ofdimples were used in each of these Examples. Details on the dimples areshown in Tables 1 to 4.

The depth of each dimple from the reference line L to the inside wall ofthe dimple was measured at 100 equally spaced points along the referenceline L from the dimple edge E to the dimple center O. The results arepresented in Tables 1 to 4.

Next, the percent change in dimple depth ΔH every 20% of the distancealong the reference line L from the dimple edge E was determined. Theresults are presented in Tables 1 to 4.

With regard to the interior construction of the golf balls in theseExamples, as shown in FIG. 6, the ball had a three-layer constructioncomposed of a core 1, an intermediate layer 2 and a cover 3. Details oneach of these layers are given below.

Core

A rubber composition containing 80 parts by weight of polybutadiene A(available from JSR Corporation under the product name BR51), 20 partsby weight of polybutadiene B (available from JSR Corporation under theproduct name BR11), 28.5 parts by weight of zinc acrylate, 1.2 parts byweight of a mixture of 1,1-di(t-butylperoxy)cyclohexane and silica(available from NOF Corporation under the product name Perhexa C-40), 4parts by weight of zinc oxide, 19.1 parts by weight of Barium Sulfate300 (from Sakai Chemical Co., Ltd.), 0.1 part by weight of anantioxidant (available from Ouchi Shinko Chemical Industry Co., Ltd.under the product name Nocrac NS-6) and 0.1 part by weight of the zincsalt of pentachlorothiophenol was prepared. The resulting rubbercomposition was molded and vulcanized in a core mold at vulcanizationconditions of 155° C. and 13 minutes, thereby producing solid coreshaving a diameter of 37.7 mm. The resulting solid cores had adeflection, as measured following compression under a final load of1,275 N (130 kgf) from an initial load of 98 N (10 kgf), of 3.6 mm.

Intermediate Layer and Cover

Using the intermediate layer material described below, an intermediatelayer having a thickness of 1.7 mm was formed by an injection moldingprocess over the cores obtained as described above. Next, using thecover material described below, a cover having a thickness of 0.8 nunwas formed by an injection molding process, thereby producingthree-piece solid golf balls having a diameter of 42.7 mm and a weightof 45.4 g. Dimples were formed on the ball surface at the same time asthe cover was molded. The intermediate layer material was a resincomposition obtained by blending Himilan® 1605, Himilan® 1557, Himilan®1706 (all ionomer resins available from DuPont-Mitsui Polychemicals Co.,Ltd.) and trimethylolpropane in the weight ratio 50/15/35/1.1. The covermaterial was a resin composition obtained by blending Pandex T-8295 (apolyurethane thermoplastic elastomer available from DIC Bayer Polymer,Ltd.), titanium oxide, Sanwax 161P (a polyethylene wax available fromSanyo Chemical industries, Ltd.) and an isocyanate compound(4,4′-diphenylmetharie diisocyanate) in the weight ratio 100/3.5/1/7.5.The intermediate layer material and the cover material had Shore Dmaterial hardnesses of respectively 62 and 47.

Performance Test

A driver (W#1) was set on a swing robot, and the height at the top ofthe trajectory (highest point attained) as well as the carry and thetotal distance traveled by the ball when struck were measured. Thestriking conditions were set as follows: initial ball velocity, about 65m/s; launch angle, about 10° ; initial backspin, about 3,000 rpm. Theclub used was a TourStage X-Drive 701 (loft, 9°) manufactured byBridgestone Sports Co., Ltd. The measured results are shown in Tables 1to 4.

It is apparent from the results in Tables 1 to 4 that, owing todifferences in the cross-sectional shapes of the dimples in the WorkingExamples and the Comparative Examples, although the heights of thetrajectories were the same, the balls in Working Examples 1 and 2 hadlonger carry distances than the golf balls in Comparative Examples 1 and2. As a result, the golf balls in Working Examples 1 and 2 traveledsignificantly longer distances than the golf balls in ComparativeExamples 1 and 2.

Japanese Patent Application No. 2016-250588 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A golf ball comprising numerous dimples formed on a surface thereof,wherein the ball has arranged thereon at least one dimple with across-sectional shape that is described by a curved line or by acombination of a straight line and a curved line and is specified bysteps (i) to (iv) below, and the total number of dimples is from 250 to380: (i) letting the foot of a perpendicular drawn from a deepest pointof the dimple to an imaginary plane defined by a peripheral edge of thedimple be the dimple center and a straight line that passes through thedimple center and any one point on the edge of the dimple be thereference line; (ii) dividing a segment of the reference line from thedimple edge to the dimple center into at least 100 points and computingthe distance ratio for each point when the distance from the dimple edgeto the dimple center is set to 100%; (iii) computing the dimple depthratio at every 20% from 0 to 100% of the distance from the dimple edgeto the dimple center; and (iv) at the depth ratios in dimple regions 20to 100% of the distance from the dimple edge to the dimple center,determining the change in depth ΔH every 20% of said distance anddesigning a dimple cross-sectional shape such that the change ΔH is atleast 6% and not more than 24% in all regions corresponding to from 20to 100% of said distance.
 2. The golf ball of claim 1 wherein, indimples having the specified cross-sectional shape, the change ΔH indimple depth reaches a maximum at 20% of the distance from the dimpleedge to the dimple center.
 3. The golf ball of claim 1, wherein dimpleshaving the specified cross-sectional shape account for at least 60% ofthe total number of dimples.
 4. The golf ball of claim 1, wherein thedimples formed on the ball surface are of at least two types ofdiffering diameter, differing depth, or differing depth and diameter. 5.The golf ball of claim 1, wherein the curved line describing thespecified cross-sectional shape of the dimple includes two or morepoints of inflection.